Bacterial chemotaxis is a complex phenomenon in which bacterial cells can detect changes in concentrations of specific chemicals, behaviorally respond to these changes, and then adapt to the new concentration of stimuli. The behavioral adaptation is associated with the reversible methylation of at least three chemotaxis specific membrane proteins called methyl accepting chemotaxis proteins, MCPs. Our peptide mapping results suggest that MCP I and MCP II each have three sites of methylation. Experiments are proposed to further investigate this question and to probe the possible mechanistic role(s) of these multiple sites of methylation. The topography of the MCPs in the bacterial inner membrane will be investigated using chemical and immunological approaches to delineate which portions of the linear sequence are in contact with the periplasm, cytosol and lipid. The chemical mechanism by which the extent of methylation of the MCPs are regulated by attractant and repellent concentrations will be investigated.